1. The National Labor Relations Act expressly forbids unions from engaging in secondary boycotts against companies not directly involved in a labor dispute.

(A) unions from engaging in

(B) the engagement by unions of

(C) unions to engage in

(D) unions from becoming engaged with（C）

(E) that unions engage upon

大全注释说只有forbid to do,所以选C。 但朗文上却有forbid sb to do和forbid sb from doing两个用法, 哪位能解释一下？谢谢